Chemical admixtures are substances other than cement, water, coarse aggregates and fine aggregates that are added to concrete mixtures to modify properties like strength and durability. They come in liquid form and are added in small dosages (<2% of cement weight). The main types are accelerating admixtures, retarding admixtures, and water-reducing admixtures. Water reducers allow a reduction in water content while maintaining the same slump and strength. Very high range water reducers can reduce water by 15-20% and are more effective than regular water reducers. Admixtures are used to achieve technical, economic or environmental benefits in concrete construction.

1. CHEMICAL ADMIXTURES

2.  DEFINATION -
 CHEMICAL ADMIXTURES MAY BE DEFINED AS
THE SUBSTANCES OTHER THAN CEMENT, WATER,
COARSE AGGREGATES, FINE AGGREGATES WHICH
ARE ADDED IN THE FRESHLY PREPARED TO
MODIFY ITS PROPERTIES LIKE STRENGTH,
DUARABILITY, etc.

3.  NEED OF ADMIXTURES-
NEED COULD BE DUE TO ANY OF FOLLOWING-
 TECHNICAL
Strength Requirement, Workability ,etc.
 ECONOMICAL
Costly things used may be replaced
 ENVIROMENTAL
Some Materials used they may not get disposed off
properly which could lead to problems like pollution,
etc.

4. IMPORTANT FACTS-
 THESE ARE AVALIABLE IN LIQUID FORM.
 DOSAGE TO BE GIVEN IS VERY SMALL (<2% by
weight of cement) SO SPECIAL CARE IS TAKEN.
 IT IS BATCHED BY VOLUME.
 CONCENTRATED ADMIXTURE IS NOT ADDED
DIRECTLY BUT THESE ARE DILUTED FIRST AND
THEN ADDED SO THAT THESE MIX THROUGH
OUT THE CONCRETE PROPERLY AND UNIFORMLY.

5. HOW TO USE ADMIXTURES-
This could be explained with the help of an example-
Let us say we want to add a dosage of 1% of admixture in
the concrete mix containing a cement of 500kg.
Therefore I will have to add admixture of 5kg.
To add this it is to be diluted using water. Let us assume I
add this in 10 liters of water . So these 10 liters are
compensated for the total amount of water to be
added that is 180 liters of total water is to be added, I
need to add only 170 liters of water and dilute solution
of 10 liters of admixtures.

6.  FUNCTIONS-
 To accelerate the initial set of concrete that is to gain
strength at early stages.
 To retard the initial set that is to keep concrete workable
for a longer time for placement.
 To enhance the workability.
 To improve penetration and reduce segregation in concrete
mixtures.
 To increase strength by reducing w/c ratio.
 To increase the durability (to enhance resistance).
 To reduce the heat of hydration.
 To inhibit corrosion and improve resistance against
chemical attack.

7. TYPES BASED ON PURPOSE-
Accelerating Admixtures-
• These are used where early strength is required
• These may also use in cold regions where we want to reduce
the setting time of concrete.
Retarding Admixtures-
• These are admixtures used where we need to increase the
setting time for the concrete to settle.
• These may also be used in hot weather where concrete sets
very early due to high temperatures.
 Slump loss may be used for analyzing the acceleration and
retardation in concrete when admixtures are used.

8.  SLUMP ANALYSIS-

9. WATER REDUCING ADMIXTURES-
 These are the admixtures which enable us to reduce
the amount of water content that is required to be
added to the concrete mix by keeping the slump same
which indirectly helps up in maintaining the same
strength and durability.

10. WHY BEST?
 These help in making the project more economical.
 These help in reducing the heat of hydration.
 These are highly effective.
Effectiveness is decided on the basis of amount of water
reduction.
If a water reducer , A on dosage of 1% reduces the water by 5-
10% of the total amount of water to be added & if a water
reducer B, on the same dosage reduces the water by 15-20%
of the total amount of water to be added then B is more
effective than A to achieve the same slump.

11. TYPES BASED ON EFFECTIVENESS
 HIGH RANGE WATER REDUCERS/PLASTICIZERS-
These are water reducing admixtures which reduce the
amount of water by 5-10% of the total amount of water
to be added.
 VERY HIGH RANGE WATER REDUCERS/SUPER-
PLASTICIZERS-
These are water reducing admixtures which reduce the
amount of water by 15-20% of the total amount of
water to be added

12. HOW TO USE WATER REDUCERS-
S. NO. WATER
(Kg/m3
CEMENT
(Kg/m3)
W/C
(%)
CA SLUMP
(cm)
STRENGTH
(M pa)
COMMENT
•1. 180 360 0.5 0 8 32 BASE
•2. 160 360 0.44 1 8 >32 HIGHER
STRENGTH
•3. 160 320 0.5 1 8 32 CEMENT
SAVING
•4. 180 360 0.5 1 >8 32 PASTICIZING
ACTION

13. AIR ENTRAINERS-
 These are used to intentionally add/entrain the air in the
concrete mix.
 It is used to improve/uniform the pore structure of the concrete.
 Air enters the concrete in form of bubbles and form the ball
bearings and hence the workability of concrete mix is improved.
 It is recommended for use in environments with cyclic, freezing
and thawing to increase the durability.
 Environments with cyclic, freezing and thawing means the
regions where water may freeze or melt due to change in
temperature.

14.  OTHERS-
 Corrosion Inhibitors such as nitrites(presence of these
ions help in improving the resistance against forces).
 Grouting Admixtures are used to prevent the rapid loss
of water to the surroundings.
 Air-detraining Admixtures are used to dissipate excess
gases and to remove a part of entrained gases.
 Shrinkage Reducing Admixtures (also called expansion
producing admixtures) either expand themselves or by
reacting with cement to expand the concrete.
 Concrete Coloring Admixtures are added to produce
colored concrete surfaces and cements.

15. QUESTIONS???